The present embodiments relate generally to phase change ink compositions, and in particular, sulfonated small molecules for use in phase change ink compositions to prevent and/or reduce printhead and nozzle contamination in ink jet printers caused by drooling and faceplate staining. Phase change ink or solid ink compositions are characterized by being solid at room temperature and molten at an elevated temperature at which the molten ink is applied to a substrate. These phase change ink compositions generally comprise an ink vehicle and a colorant, and can be used for ink jet printing.
Phase change ink or solid ink printers conventionally receive ink in a solid form, which is sometimes referred to as ink sticks. The ink sticks are typically inserted through an insertion opening of an ink loader for the printer and are moved by a feed mechanism and/or gravity toward a heater plate. The heater plate melts the phase change ink impinging on the plate into a liquid that is delivered to a printhead assembly for jetting onto a recording medium. The recording medium is typically paper or a liquid layer supported by an intermediate imaging member, such as a metal drum or belt.
A printhead assembly of a phase change ink printer typically includes one or more printheads each having a plurality of ink jets from which drops of melted phase change ink are ejected towards the recording medium. The ink jets of a printhead receive the melted ink from an ink supply chamber, or manifold, in the printhead which, in turn, receives ink from a source, such as a melted ink reservoir or an ink cartridge. Each ink jet includes a channel having one end connected to the ink supply manifold. The other end of the ink channel has an orifice, or nozzle, for ejecting drops of ink. The nozzles of the ink jets may be formed in an aperture, or nozzle plate that has openings corresponding to the nozzles of the ink jets. During operation, drop ejecting signals activate actuators in the ink jets to expel drops of fluid from the ink jet nozzles onto the recording medium. By selectively activating the actuators of the ink jets to eject drops as the recording medium and/or printhead assembly are moved relative to each other, the deposited drops can be precisely patterned to form particular text and graphic images on the recording medium.
One difficulty faced by fluid ink jet systems is that organic pigments and dyes used in the phase change inks show drooling behavior and faceplate staining in the printhead. Drooling is defined as the burst of the ink out of the printhead when pressure is applied and is expressed in inches water in the Low Pressure Assist cycle (LPA). Staining represents the fouling of the faceplate by the ink.
A synergist or a pigment stabilizer is a compound that promotes the adsorption of the polymeric dispersant onto the pigment. For example, in the case of a cationic dispersant, the dispersant anchor is comprised of a positive charge and will interact with an anionic group present on the synergist, exchanging counter ions and promote an anchoring of the dispersant onto the modified pigment surface. Solid inks containing a pigment/dispersant package show drooling behavior and faceplate staining in the printhead, even at low applied pressures and in some cases, such pigmented inks show auto-drooling behavior which is an extremely undesirable property of an ink. Changing pigments, dispersants, and the use of synergist with the pigment to enable dispersion stabilization did not successfully improve drooling and staining.
Experimental trials indicated that one approach for solving drool and staining of the faceplate by solid ink could be use of compounds containing acid groups. Commercially available compounds, however, tend to be very polar in nature and cannot be used as such compounds exhibit a strong gelling behavior in solid ink. For example inks prepared with commercially available synergists SOLSPERSE 5000 (a derivatized sulfonated copper phthalocyanine) and SOLSPERSE 22000 (a derivatized sulfonated analog of Pigment Yellow 12) at nominal ink loadings below 1% by weight (with no pigment added) showed no drooling or staining behavior. However, when the synergist loading was increased at or above 2.5% wt (with no pigment added), the inks displayed strong gelling behavior.
Because these commercially available synergists cannot be used as colorants or as anti-drooling additives, there is a need for finding other compounds containing acid functional groups to address the problems discussed above while being compatible for use in phase change inks.